The homeostatic mechanism in the inner ear fluids, perilymph and endolymph, was biochemicallyinvestigated and reviewed.Glucocorticoid receptor (GR) and its mRNA expressions in the cochleaof guinea pig were also investigated. Results and conclusions were as follows:
1) The salient feature of the cochlear fluid composition is the high K⁺ (157mM), low Na⁺ (1.3mM), and low Ca²⁺ (0.023mM) content of endolymph. In contrast, the ionic contents of perilymphlargely conform to those of other extracellular fluids. Aspartate and glutamate were significantlyhigher in endolymph than in perilymph. All other amino acids investigated were significantly lowerin endolymph by an order of magnitude. Amino acid levels were all higher in perilymph than incerebrospinal fluid (CSF); two by an order of magnitude. The content of metallic elements in CSFwas very similar to that in perilymph except for zinc, in which the concentration was significantlylower in CSF than in perilymph (p<0.01). The concentration of iron in endolymph was the highestamong those in the inner ear fluids, CSF and serum (p<0.01).
2) There was a steep gradient of glycine content between perilymph and CSF. The longitudinalflow in perilymph was 2 nl/min or less. There was a pronounced difference in the pharmacokineticsof furosemide between CSF and perilymph. Furthermore, probenecid, one of the competitive inhibitorsof an organic anion transport, inhibited an active transport of furosemide through the blood/perilymph barrier, though there was a steep gradient of furosemide concentration between these twocompartments. These results suggest that perilymph can be derived from blood.
3) In contrast to the drastic reduction of EP, the ionic contents of endolymph in the experimentallyinduced hydropic ear have been reported to be constant except for Ca²⁺, of which concentrationin the guinea pig increased 8 weeks after induction of hydrops. In perilymph of the hydropic ear, the concentration of Ca²⁺ decreased 8 weeks after induction of hydrops.
4) The distribution of GRs in the cochlea of guinea pig was studied by immunohistochemistry.GRs were observed in the spiral ganglion, spiral limbus, stria vascularis and spiral ligament. Withthe use of original primer of guinea pig, the expression levels of GR mRNA in the cochlea of guineapig were also investigated by reversed transcriptase polymerase chain reaction. The highest expressionlevel of GR mRNA was recognized in the modiolus. Acoustic over-stimulation with 120 and130 dB SPL for 10 min significantly reduced the expression level of GR mRNA in the cochlea at 2hours after stimulation.

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the rat cochlea and endolymphatic sac (ES) was examined by PCR and in situ hybridization.After reverse-transcription of mRNA of the rat cochlea and ES, cDNA was amplified by PCRusing pairs of primers specific to these receptors. After subcloning of the PCR products, the nucleicacid sequences was determined. Next, localization of the expression of these receptors in the cochleaand ES was examined by in situ hybridization. Expression of vasopressin Vla, V2, ANP-A, ANP-B and aldosterone receptors was detected in the cochlea by PCR. Expression of the Vla and ANP-A receptors was detected in the ES by PCR. The expression of following receptors was determinedby in situ hybridization: ANP-A receptor in the cochlear nerve root, ANP-B receptor in thespiral ganglion and aldosterone receptor in marginal cells of the stria vascularis and in epithelialcells of the intermediate portion of the ES. These results suggest that vasopressin, ANP and aldosteroneplay certain roles in the cochlea as well as in the ES. In particular, it seems possible that ANP plays a role in the function of the cochlear nerve and that aldosterone plays a role in the productionand absorption of endolymphatic fluids.

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It is well known that vasopressin (antidiuretic hormone) plays an important role in variousorgans. Many evidence have accumulated to suggest that vasopressin plays a possible role withregard to inner ear pressure changes.
We demonstrated renal type (V2) argine vasopressin (AVP) receptor, C-type natriuretic peptideand it's receptor, vasoactive intestinal polypeptide and it's receptor mRNA were present in the ratinner ear using an assay of reverse transcription and polymerase chain reaction (RT-PCR), and alsodemonstrated with immunohistochemical studies.
Another study was undertaken to demonstrated down regulation of AVP-V2 receptor when AVPwas administered.
From these results, we expect a water regulation system of inner ear. This system will beregulated mainly by vasopresin. Consequently, disorder of this system is thought to be a cause ofendolymphatic hydrops of Meniere's disease.

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Recently, a considerable accumulation of evidence has been presented which suggests a possiblehormonal control of the inner ear. Vasopressin or corticosteroid may play an important role in theregulation of ion and water. In the present report, it was clinically and experimentally examinedhow the excess of these hormones might cause any influences on ion and fluid homeostasis in theinner ear. The results were as follows: 1) The clinical survey revealed that plasma vasopressin waselevated not only in cases of Meniere's disease but also in cases of the other diseases with endolymphatichydrops. Especially, it must be noted that high levels of plasma vasopressin were often observedin cases of unilateral juvenile deafness, which was thought to develop delayed hydrops in courseof time. This leads the assumption that the elevation of plasma vasopressin level in these diseasesseems to be one of the most causative factors in the formation of endolymphatic hydrops. 2) Vasopressinadministration produced endolymphatic hydrops in guinea pigs. The endolymph volume increasedin proportion to plasma vasopressin levels. On the other hand, experimentally induced endolymphatichydrops reduced by an application of V₂-antagonist. 3) Endolymphatic hydrops was alsoinduced by an administration of glucocorticoid as well as by that of aldosterone. 4) Microperoxidaseuptake and transport in the marginal cells was accelerated in the animals treated with aldosterone.Since the uptake of microperoxidase is thought to represent water phase endocytosis., aldosterone, amediator of Na-K ATPase, might play a possible role in regulaion of water and water-soluble materialin the cochlea. These results support the assumption that water and ion regulation in the innerear is controlled by vasopressin and/or corticosteroids and that the excess of these hormones may beone of the possible factors in the formation of endolymphatic hydrops.

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In the previous study, we have identified the expression of AQP-2 and AQP-3 water channels inthe rat inner ear. Both molecules have predominantly been expressed in supporting cells justbeside the organ of Corti of the cochlea, and in the epithelium of distal portion of the endolymphaticsac. To address regulation of the expression of AQP-2 and AQP-3 by vasopressin (AVP), we employedcompetitive PCR analysis and imaging analysis with the inner ear of rats treated with a 7-day infusion of AVP. In response to AVP, AQP-2 and AQP-3 mRNAs were up-regulated severalfolds, while V2 receptor mRNA was exclusively down-regulated and dropped under the detectablelevel for RT-PCR. As the expression of AQP-2 and AQP-3 mRNAs higer, the volume of the endolymphaticspace in the cochlea became lesser. Instead of a stable expression of these two molecules, however, down-regulation of V2 receptor mRNA rather resulted in an increase in the volume of theendolymphatic space. These results suggest that AVP regulates the expression of AQP-2 and AQP-3mRNAs in the inner ear, and that AVP-regulated water channels may be one of the essential factorswhich determine the volume of the endolymphatic space.

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It is generally accepted that the stria vascularis produces K⁺-rich endolymph and the positive endocochlearpotential (EP).In spite of the critical role of EP in normal function of the cochlea, thecellular mechanism underlying the production of EP has not been agreed upon.In this report, iontransporters in the basolateral membrane of marginal cells and a K⁺-conductance which is thought tobe responsible for the generation of EP are reviewed, and relevance of the two-cell model (five compartmentmodel) of the stria vascularis is discussed.

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The stria vascularis is an important tissue responsible for the production of endolymph.It isthought that a number of mechanisms for ion transport exist there.Polymerase chain reaction (PCR) has enabled us the molecular biological research of the cochlea in spite of the limited amountof tissue.To investigate the strial ion transport, we examined the expression and localization of them RNA of ion channels and transporters using molecular biological techniques.PCR and in situhybridization suggest that Cl channels, Na-K-Cl cotransporters, Na-H exchangers and Na-Ca exchangersplay important roles in strial ion transport.

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To determine the indication of cochlear implant, an electrical auditory test on the promontry isperformed to investigate sense of sound at the auditory nerve or the nerve terminal. However, theroutinely used promontry stimulation test requires penetration of the tympanic membrane. Becauseof this harmful procedure, the promontry stimulation test is not easy to apply to normal subjects.
Recently, one electroaudiometer has developed by MED-EL which has adopted a non-invasivemethod. A silver ball electrode is placed near the tympanic membrane to give electrical stimulationto the cochlea.
Using this procedure, we investigated how people with normal hearing can feel electrical stimulation.Our results showed that no one could feel the stimulation as sound at low frequency of electricpulse, but considerable number of people could feel the stimulation as real sound at high frequencyof electric pulse. This auditory sensation could possibly be caused by electrophonic effect.
This electroaudiometer with a silver ball electrode is less harmful and easily used for varioussubjects.

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In order to reconstruct the ossicular chain, numerous techniques using different prostheses havebeen proposed. However, there are few studies to investigate the transmission characteristics of theseprostheses, and information that could lead to the design and development of better ossicular replacementprostheses is absent in these reports.
Clinical trials comparing two or more prostheses would be the best analytical method, but theseare difficult to perform and are contaminated by a large number of variables that are hard to control.Therefore, some experiments with ossicular substitution in human temporal bones have been performed.However, the temporal bone is also difficult to handle. On the contrary, application of the Finite Element Method (FEM) enables complicated irregular geometries of biological structures to bemodeled easily, and it also enables their dynamic behavior to be understood in detail without experiments.
In this study, three-dimensional FEM models of a human intact middle ear and reconstructed middleears using an incus replacement prosthesis (IRP) were established by applying the FEM programdeveloped by our group. Then, the effects of the materials, shape and contact point of theIRP on the transmission characteristics and vibration mode of the middle ear were analyzed. Thefollowing conclusions were oblained:(1) High stiffness of the IRP increases the transmission factorfor higher frequencies.(2) The best contact point of the IRP is the malleus manubrium, especially forhigh frequencies above 1.5kHz, whereas the contact of the IRP at the inferior portion shows theworst performance for frequencies ranging from 0.7 to 2.5kHz.(3) There is an optimum value ofthe cross-sectional area for the IRP made of tragal cartilage.

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Twin sisters were very similar in their clinical findings of the normal auricles and external auditorycanals. They had no other abnormalities but conductive hearing loss. Helicalscanning CT successfullyrevealed the stapes superstructures. Careful Stapedectomy was performed in their right earresulted in remarkable hearing improved about 40dB in both cases. Microscopic examination foundthe immature cartilage at the edge of the foot plates suggested the possibility of the cause of thestapes fixation.

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We report a case of unilateral sensorineural hearing loss in a 55-year-old female with sarcoidosis.The site of the lesion for hearing loss was investigated by electrocochleogram (ECochG) and evokedotoacoustic emission (EOAE).She showed progressive hearing loss with some fluctuation.We recordedECochGs and EOAEs twice during the follow-up period. She showed elevated pure tone thresholdsat 4kHz at the first examination. We speculated that the site of the lesion for hearing loss was notouter hair cells but the acoustic nerve, and that the hearing loss was caused by impairment in activeprocess. It was not certain whether the hearing loss was associated with sarcoidosis or not. Thepure tone average level was 73.8dB at second examination. It is estimated that at that time hearingloss could be the result of damage to outer hair cells.

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Osteomas of the temporal bone are relatively rare. A 13-year-old male was complaining of anenlarged mass in the right retro-auricular region. CT examination demonstrated an osteogenic tumorarising from the cortical area of the right temporal bone. The tumor was surgically removed andwas found to be originating from the bony wall of the mastoid portion of the temporal bone.
The size of the tumor was 2.5×3.0cm weighed 4.7g. The tumor was microscopically diagnosedas osteoma. Fifteen cases of osteoma of the temporal bone including our case have been reportedfrom 1959 to 1997 in Japan.

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A 34-year-old man manifested left facial palsy the following day and right facial palsy severaldays after a motorcycle accident. On 12 days after the injury, he showed complete bilateral facialpalsy and no response on electroneuronography bilaterally. The audiogram revealed a left C⁴-diphearing loss, and CT scan demonstrated bilateral temporal bone fracture. He was treated with highdosesteroid therapy, and then underwent transmastoid facial nerve decompression on the left side.The facial movement gradually improved after the treatment, and completely recovered 173 daysafter the injury.

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